1. Field of the Invention
The present invention relates to a data transmitting apparatus and method, a data receiving apparatus and method, and a data transmitting/receiving system and method, and more particularly to those adapted to prevent illegal use of data in transmitting and/or receiving the data via a 1394 serial bus.
2. Description of the Related Art
Recently, there is noticed widespread application of the IEEE 1394 high performance serial bus (hereinafter referred to simply as 1394 bus) standardized by the IEEE. In such 1394 bus, digital video and audio signals can be transmitted fast together with control commands in real time via a single cable by connecting thereto electronic apparatus such as audio-visual (AV) apparatus and a personal computer.
In transmission of data via a 1394 bus, there are known an asynchronous mode (asynchronous data transmission mode) and an isochronous mode (synchronous data transmission mode) where the data are synchronous with isochronous cycles of 8 kHz (125 xcexcs) generated by a cycle master in the 1394 bus. Commands are transmitted generally in an asynchronous mode, while video and audio signals are normally transmitted in an isochronous mode due to the necessity of real time reproduction.
However, data transmission in the isochronous mode is performed through multi-address communication where a destination of the data is not specified. For this reason, when any video or audio signal to be protected with respect to the copyright is transmitted via a 1394 bus, there arises a problem that some users not permitted by the relevant copyrighter may copy such video or audio signal illegally or may change or modify the copied signal.
It is therefore an object of the present invention to realize exact prevention of any illegal use of such data.
According to a first aspect of the present invention, there is provided an apparatus for transmitting data in a first or asynchronous mode and a second or isochronous mode. This apparatus comprises a means for ciphering the data to be transmitted by the use of cipher keys; a means for packetizing the ciphered data into packets of the isochronous mode; and a means for transmitting the output of the packetizing means. In this apparatus, transmission of the data is performed in conformity with the IEEE 1394 protocol, and the packetizing means attaches, to a header of the ciphered data, an identification code relative to the ciphering. The cipher keys consist of a session key invariable in each session of the data to be transmitted, and a time variable key updated in each session. Information relative to the time variable key is contained in each packet of the isochronous mode, and information relative to the session key is also contained therein.
According to a second aspect of the present invention, there is provided a method of transmitting data in a first or asynchronous mode and a second or isochronous mode. This method comprises the steps of ciphering the data to be transmitted by the use of cipher keys; packetizing the ciphered data into packets of the isochronous mode; and transmitting the packetized output. In this system, transmission of the data can be executed with enhanced security.
According to a third aspect of the present invention, there is provided an apparatus for receiving data transmitted thereto in a first or asynchronous mode and a second or isochronous mode. This apparatus comprises a means for receiving the transmitted data; a means for depacketizing the output packets obtained from the receiving means; and a means for deciphering the ciphered data outputted from the depacketizing means. In this apparatus, transmission of the data is performed in conformity with the IEEE 1394 protocol, and the depacketizing means separates an identification code relative to the ciphering from the received data. The cipher keys consist of a session key invariable in each session of the data to be transmitted, and a time variable key updated in each session. Information relative to the time variable key is contained in each packet of the isochronous mode, and information relative to the session key is also contained therein. Therefore, the data transmitted with security can be deciphered exactly.
And according to a fourth aspect of the present invention, there is provided a method of receiving data transmitted in a first or asynchronous mode and a second or isochronous mode. This method comprises the steps of receiving the transmitted data; depacketizing the output packets obtained in the receiving step; and deciphering the ciphered data outputted in the depacketizing step.
Thus, it is possible to realize improvements in transmission and reception of the data with enhanced security.